This invention relates to pneumatic tires and more particularly to a pneumatic insert structure positioned within the air chamber of a pneumatic tire for supporting load and maintaining the tire on its rim when the tire is deflated.
Present day pneumatic tires commonly utilize an inner tube to contain air or they are tubeless. In the latter type of tire, the beads of the tire are seated tightly against the wheel rim, and the wheel and the tire together form a sealed air containing chamber. Puncture of either a tubeless or tube type tire on a vehicle will result in the deflation of the tire to a "flat" condition and a number of consequent problems for the operator of the vehicle. If any attempt is made to run on the flat tire for more than a very short distance, the tire will rapidly deteriorate. Thus, the flat tire has to be replaced with another tire usually carried as a spare in passenger type vehicles. Considerable difficulty is often involved in replacing a flat tire with a spare tire. Many people do not have the strength and sometimes the know-how to remove a tire and replace it with another, spare tire. Also, removing a tire and putting a spare tire on a vehicle can be quite dangerous on busy highways and streets.
Another critical problem when tire deflation is rapid is the possible loss of control of the vehicle. The danger is caused by the loss of stability of the tire when it rapidly collapses and the tire beads are released to move off of their seats on the wheel rim.
A wide variety of tires and associated "run-flat" tire structures have been offered as solutions to these problems. These solutions include, (1) a multi-chambered tube in which a number of chambers will remain inflated if one is punctured and loses air, (2) an inner tube-like structure occupying less than all of the tire interior space that is not readily punctured due to its being remote from the tire tread area, (3) a diaphragm similar to a tube spaced from the tire tread, but which is not a completely enclosed chamber and has the ends of its sides sealed against the tire in the bead region and, (4) a solid structure mounted on the wheel, usually annular in shape, bearing against the tire bead and extending above the rim.
The multi-chambered inner tube has not been successful due to its complexity and resulting high cost and manufacturing difficulty. This type of tube also adds considerable bulk to the tire and increases its operating temperature. A solid run-flat support structure typically has at least one and frequently both of the problems of complexity and difficulty in mounting due to the problem of clearing the wheel rim. The pneumatic diaphragm has not been successful due to lack of reliability of the seal against the tire bead and the complexity and mounting difficulty incurred when attempting to assure the seal by means such as clamping the diaphragm ends between the rim and bead. Drawbacks of both the completely enclosed inner tube-like structure and the diaphragm, where they occupy less than all of the tire interior space, include excessive contact with the interior crown region of the tire, the bead region, and the radially inward sidewall region of the tire during normal inflated load carrying conditions which causes deterioration of both tire and the support structure. Also, prior pneumatic run-flat support structures frequently permit excessive deflection of the tire when it is deflated to cause its rapid deterioration. A further problem of pneumatic type run-flat structures is material fatigue which causes their rapid deterioration when the tire is deflated and the run-flat structure is carrying load. This problem is due in part to the difference in circumference between the tread of the tire and the run-flat structure. As the tire rotates through its tread patch (the portion of the tire in engagement with the road surface), the greater distance that the longer tread must travel relative to the run-flat structure causes buckling of the tire and scuffing, bumping movement relative to the wheel rim of the run-flat structure.
With respect to the prior art, the closest prior art of which the applicant is aware is U.S. Pat. No. 3,941,176, United Kingdom Pat. No. 658,465, and Canadian Pat. No. 625,562. Copies of each of these patents are enclosed with this patent application.
U.S. Pat. No. 3,941,176 is relevant in that it discloses a fully enclosed pneumatic chamber positioned within the air cavity of a tire. The inner chamber is made of a thermoplastic elastomer material and has a volume in excess of 50% of the volume of the tire cavity volume. In this construction, the distance between the crown region of the inner chamber and the tire surface radially inward of the tread is stated to be not critical. On the contrary, however, it is believed that this distance is critical due to the problem of engagement with and scuffing of the inner crown region of the tire by the inner chamber. Further, an inner chamber volume of 50% or more of tire cavity volume will result in considerable scuffing of the tire inner crown region, bead region and sidewall region by the inner chamber during normal inflation and load carrying conditions of the tire.
In United Kingdom Pat. No. 658,465, there is disclosed a safety tube which occupies at least 30% of the air space within the tire but not the entire space within the tire. The sidewall of the safety tube engages the bead region and the lower sidewall region of the tire. The problem with this type of run-flat tube construction is also that it will interfere with the sidewall action of the tire during normal inflation and load conditions and will permit excessive deflection and consequent deterioration of the tire when the latter is deflated and the safety tube is carrying the load.
In Canadian Pat. No. 625,562, there is disclosed a diaphragm which is anchored in place and sealed against the beads of the tire by wrapping the edges of the diaphragm around the bead and clamping them between the wheel rim and the bead when the tire is seated. The volume of the air in the compartment formed by the diaphragm and rim comprises 60% of the volume of the air in the space formed by the inner surface of the tire and the rim. The tire deflects not more than 25% of its height radially outward of the rim flanges when it is in a deflated condition. The sidewall of the diaphragm extends along the bead region and into the radially inward sidewall region of the tire. Thus, in this construction also, there will be interference with the functioning of the sidewall. Also, minimizing the deflated tire deflection is accomplished by utilizing a diaphragm compartment volume of 60% of the volume of the compartment formed by the tire and rim.
In the detailed description of the invention following hereinafter, the section height of the tire is used as a reference value for describing or measuring distances and the amount of deflection of the tire and insert structure. The term "section height" of the tire as used herein means the height of the section of a new tire, where the section is in a plane passing through the axis of the tire and through the tread patch of the tire, and the height is in a radial direction perpendicular to the axis of the tire between the most radially outward edge of the rim flange of the wheel on which the tire is mounted and the most radially outward part of the tread of the tire when the tire is inflated to its rated inflation pressure and supporting its rated load.